The invention relates to a method of controlling an internal combustion engine with a common rail fuel injection system including for the cylinders individual storage chambers, wherein, during a measuring interval defined particularly by crankshaft angles, a fuel pressure is determined and stored and any significant change of the fuel pressure in a storage chamber is interpreted as the beginning or the end of a fuel injection.
In an internal combustion engine, the begin and the end of the fuel injection determines to a large extend the quality of the combustion and the composition of the exhaust gases. In order to maintain the legal limit values, these two characteristic values are generally controlled by an electronic control unit. However, in practice, in connection with a common rail fuel injection system, there is the problem that there is a certain time delay between the energization of the injector, the needle stroke of the injector and the actual begin of fuel injection. The same applies correspondingly to the end of the fuel injection.
A measure for alleviating the problems resides in the detection of the armature movement that is its impact at an end position thereof. Such a solution is known for example from DE 42 37 706 A1. Another possibility for detecting the impact of an armature can be obtained by applying a measuring current to the injector winding during the armature travel phase. By the measuring current, a magnetic field is generated in the winding which changes upon armature impact. The magnetic field change results in a detectable induction voltage. Such a solution is described for example in DE 44 33 209 A1. Both measures have been found suitable in practice. However, the individual properties of the cylinders and the injectors cannot be detected with these measuring methods. A corresponding control measurement for timing the control parameters is technically complicated and is therefore not done in connection with mass-produced engines. The same is true for the direct needle stroke measurement by a travel distance sensor.
Another measure for alleviating the problem mentioned above is disclosed in DE 31 18 425 A1. In this publication, the pressure pattern in the rail is measured and the values are then filtered by a differentiation of the filtered pressure pattern. Significant changes, that is, value extremes are interpreted as injection begin and injection end. The filtering of the measured pressure pattern is absolutely necessary since spurious signals such as the injection frequency and the pumping frequency of the high pressure fuel pump affect the pressure signal. However, filtering the signal results in a certain time delay with respect to the base signal.
DE 43 44 190 A1 discloses an internal combustion engine with a common rail system wherein a separate storage chamber is provided for each injector.
It is the object of the present invention to provide a common rail fuel injection system with individual storage chambers wherein the begin of the fuel injection into the cylinders and the end of the fuel injection can be relatively accurately determined.